Hydronic Heaters are typically located outside the buildings they heat in small sheds with short smokestacks. They burn wood to heat liquid (water or water-antifreeze) that is piped to provide heat and hot water to occupied buildings such as homes, barns and greenhouses. However, hydronic heaters may be located indoors and they may use other biomass as fuel (such as corn or wood pellets).
Phase 2 White Tag
When buying a hydronic heater, look for the white tag. The Phase 2 white tag is for qualified models that are about 90 percent cleaner than unqualified models.
Although most units are designed to burn dry, seasoned wood, some people use them to burn green wood, which generates much more smoke. Others burn household trash or construction debris, which not only release harmful chemicals and pollution, but can be against state law.
Unqualified hydronic heaters can be substantially dirtier and less efficient than most other home heating technologies. With their smoldering fires and short smokestacks (usually no more than six to ten feet tall), hydronic heaters create heavy smoke and release it close to the ground, where it often lingers and exposes people in the area to nuisance conditions and health risks.
EPA has initiated a voluntary program for manufacturers of hydronic heaters. EPA’s primary intent is to first encourage manufacturers to produce cleaner hydronic heater models. EPA also wants those who buy a hydronic heater to buy the cleanest models available, which are those that qualify for the EPA voluntary program.
This program encourages manufacturers to produce and sell cleaner, more efficient hydronic heaters. To participate in the hydronic heaters program, manufacturers commit their best efforts to develop cleaner models, approximately 90 percent cleaner for Phase 2 white hang tag. List of EPA-qualified hydronic heaters*
Information for Consumers
- Look for the Phase 2 white tag (about 90 percent cleaner) (PDF) (1pg, 281k, About PDF) when purchasing a hydronic heater
- List of EPA-qualified hydronic heaters*
- Understanding the white tag
- Frequently Asked Questions (PDF) (5pp, 33k, About PDF)
* The wood-burning appliances that are "qualified" under the EPA's Voluntary Fireplace Programs are not "certified" per EPA's Wood Heater New Source Performance Standard. Contact your state or local air quality agency for clarification on the type of wood-burning appliances, if any, that may legally be installed in your area.
Check Your State and Local Ordinances
Hydronic heater emissions are a significant concern in many local areas. Numerous scientific studies report potentially serious adverse health effects from breathing smoke emitted by residential wood combustion. Residential wood smoke contains fine particles, which can affect both the lungs and the heart. In some areas, residential wood smoke can be a significant source of exposure to fine particle pollution.
Many local agencies have developed ordinances that ban unqualified hydronic heaters and establish minimum distances to neighbors and minimum stack heights. EPA has provided technical and financial support for the Northeast States for Coordinated Air Use Management (NESCAUM) to develop a model rule that state and local agencies can use to regulate hydronic heater emissions. To learn about state regulations, visit The Vermont Department of Environmental Conservation, Air Pollution Control Division's page of state-by-state regulations governing hydronic heaters.